Bioreactors are common laboratory and industrial installations used in the areas of cell culture, chemical production, fermentation, testing and analysis, and other biological processes well known to those skilled in the art. A problem inherent in such bioreactors is the need to control the ingress and egress of various compounds to and from the bioreactor. As the size and volume of bioreactors decrease, or as the need to control becomes increasingly exacting, problems occur in the need to precisely control, over a long period of time or in respect of very small quantities of certain compounds, the movement of molecules both into and out of the bioreactor.
Various means have been employed to control small flows of fluids, in a field generally called microfluidics. In general, the means have proposed mechanical devices that are designed to mechanically, but accurately, deliver very small amounts of a fluid through various microchannels to a delivery point. A typical example is seen in U.S. Pat. No. 6,810,713; in which rotors periodically squeeze the microchannels formed in an elastic polymeric substrate to propel small amounts of fluid towards a delivery point by their compressive effect on the microchannel. Another approach is seen in U.S. Pat. No. 6,797,187; in which an electromagnetic field is used to generate a flow of a fluid in a microchannel lined, at least in part, with silicon nitride. Yet another approach is seen in U.S. Pat. No. 6,743,636; wherein pneumatically driven Venturi pumps move fluid through a microchannel system.
These approaches, and others that form the present art, rely on the movement of fluid volumes, albeit small ones, in order to transfer the various components that may be present in such fluids. Therefore, they fall prey to a myriad of problems. As the scale of the device decreases, it becomes increasingly difficult for a mechanical, or even electro-mechanical, device to control the very slow movement of molecules. Even slight variations in the operation of the various pumping mechanisms will result in wide swings, in a relative sense, in the amount of fluids transferred. The instant invention, on the other hand, is novel in its approach to controlling the displacement of various molecules into and out of a bioreactor system by controlling the rate of diffusion at an interface between two fluids, while minimizing any actual mixing of the fluids themselves. Therefore, the delivery of various molecules is inherently stable and predictable, and simple variations in the structure of the bioreactor suffice to control this diffusion.